The Interactive Mathematics Program (IMP) has developed a new four-year high school curriculum which is organized around units lasting from 5 to 8 weeks. Each unit centers on a rich problem, and students develop new concepts and skills by solving that central problem. Graphing calculators play an important role in the IMP curriculum, involving simulations, curve-fitting, operations with matrices, and programming. Examples of the use of calculators in the curriculum and guiding principles for their use are given in these papers.